Finite element models of passive continental margins with implications for the initiation of subduction zones

Abstract

Passive continental margins are in general characterized by the lateral contrast between oceanic and continental lithosphere and by the presence of thick sedimentary deposits which cause flexure and stressing of the lithosphere. Passive margins therefore, are potential sites for plate rupture and initiation of subduction. To investigate the evolution of passive margins, we have constructed finite element models, in which we have incorporated a complex system of forces, depth-dependent rheological properties and lateral variations across the margin. Sediment loading generates differential stresses of several kilobars and dominates the state of stress at passive margins. Stresses of this order of magnitude may cause failure of the lithosphere and initiation of subduction. We have found that the aging of passive margins alone does not make them more susceptible to initiation of subduction. However, extensive sediment loading on young lithosphere might be an effective mechanism for closure of small oceanic basins. This phenomenon plays an important role in the process of mountain building.